Recent trends have developed two major factors in the design of industrial facilities, i.e., the increasingly stringent governmental pollution control requirements, and the cost and availability of energy. Particularly difficult problems in this regard are found in the design of paint spray booth facilities for the application of paint to automotive bodies and similar products, due to the enormous volumes of air flow required in the paint spray booths in industry.
The pollution problems are associated primarily with the organic liquid constituents, including solvents, thinners and diluents of paints. Such liquid constituents are vaporized during the paint application, which vapors pass into air circulated through the booth. Such air must be circulated at relatively high volume in order to enable the paint sprayers to work in a safe, healthful and clean environment.
The rigorous standards of emissions applied to industrial facilities precludes the discharge of such organic or solvent vapor laden air directly into the atmosphere, and such vapors in the discharged air are required to be reduced to very low levels.
A common approach in eliminating such vapors which are combustible is to incinerate the same by passing the air inyto an incineration chamber which is heated by a burner to raise the temperature of the air sufficiently to cause oxidation of, for example, the hydrocarbons into carbon dioxide and water vapor prior to being exhausted to the atmosphere.
However, for the enormous air flow rates exhausted from paint spray booths, the incineration process requires vast expenditures of energy, thus rendering this solution very costly to implement.
Another alternate approach which has been attempted and considered in this context is the use of adsorber beds such as of activated charcoal, over which the exhaust air is passed for direct adsorption of the solvent vapors, thus enabling their elimination from the exhaust air.
Again, the enormous air volumes in automotive production and similar applications and the need to regenerate the adsorber beds render this approach extremely expensive.
Yet another approach which has been proposed involves the replacement of the organic solvent based paint with water based paint, the elimination of vapors thus enabling direct discharge of the exhaust air to the atmosphere, after filtration or other treatment of the air to remove the paint solids.
While effective in this regard, the water based paints require close control over the temperature and humidity of the air supplied to the booth, with air cooling and dehumidification during summertime, and heating and humidification during wintertime operation. This psychrometric control requires considerable capital investment and furthermore entails considerable energy to execute.
Certain advances have been made in reducing the solvent content of paints and also in the paint application process to reduce the quantity of organic solvent vapors escaping, but there has not been provided a relatively simple, inexpensive and reliable means for eliminating the organic emissions which does not entail excessive expenditure of energy when eliminating relatively low concentrations of solvents. Such low concentrations are a result of the working conditions in which large volumes of ventilating air are passed into the spray booth. These large volumes of fresh air flow must be warmed during wintertime operation and then exhausted to the atmosphere, representing a large energy loss.
Accordingly, it is an object of the present invention to provide a system and process for the elimination of organic vapors at relatively low concentrations, i.e., a few hundred parts per million, from the air exhausted from a paint spray facility in which the equipment required is relatively inexpensive to install and operate.
It is a further object of the present invention to provide an absorption system which is adapted to accommodate the great volumes of air flow involved in typical automotive paint spraying installations.
A still further object of the invention is to provide a solvent absorption system as described above which may be integrated into a paint spraying operation so as to minimize the energy requirements involved in the absorption process.